Smooth muscle cell PRDM16 and aortic aneurysm

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Project Summary/Abstract Aortic aneurysm (AA) is an asymptomatic disease with high mortality rate (65% to 85%) if rupture occurs. Repair through open or endovascular surgery is currently the only therapeutic option for aortic aneurysm. No drug has been approved for the treatment of this devastating disease. While surgical intervention is effective in preventing rupture, it is however often associated with surgical complications that result in severe morbidity and even mortality. Thus, AA is still a life-threatening disease. Unfortunately, the mechanisms underlying aneurysm development are largely unknown, which is limiting development of medications for treatment of aneurysms and dissections. This highlights an urgent need for better understanding of aneurysm formation and progression. PR domain containing 16 (PRDM16) is a transcriptional regulator and plays crucial roles in the determination and development of cells including hematopoietic, cardiomyocytes and smooth muscle cells. Prdm16 germline or vascular smooth muscle cell (VSMC) selective knockouts are embryonic lethal in mice, highlighting the importance of PRDM16 in the developmental processes of VSMC. It is not yet known whether PRDM16 in VSMC will affect the development of abdominal aortic aneurysm (AAA). Our preliminary data indicate that PRDM16 is significantly reduced in aorta of AAA patients and the PRDM16 SNP is associated with human AA rupture. Tamoxifen-induced VSMC-selective Prdm16 knockout in mice results in a significant increase in elastin degradation in AAA lesions. These data suggest that loss of PRDM16 function promotes AAA formation. We further uncovered that PRDM16 negatively regulates expression of transforming growth factor β (TGF-β) and A disintegrin A metalloprotease 12 (ADAM12) in VSMC. TGF-β induces ADAM12 expression which is positively correlated with cell apoptosis. Additionally, conjugated linoleic acid (cLA) is an omega-3 derivative that serves as the preferential endogenous substrate of nitration. Interestingly, oral delivery of cLA and inorganic nitrite (NO2) yields endogenous nitrated cLA (NO2-cLA). NO2-cLA is a next generation nitro-fatty acid and the most abundant endogenously produced in humans. Our preliminary data document that NO2-cLA stabilizes PRDM16 protein and protects against AAA formation and progression in vivo. Also, NO2- cLA inhibits VSMC apoptosis and inflammation, two hallmarks of AAA, in a PRDM16-dependent manner. Therefore, we will specifically and systematically address the central hypothesis that “endogenous production of NO2-cLA protects against AAA formation and progression through PRDM16 in VSMC”. The specific aims of this proposal are to: 1) determine that PRDM16 in VSMC prevents AAA formation and progression; 2) determine that PRDM16 protects against VSMC dysfunction through inhibition of TGF-β/ADAM12 signaling; and 3) determine that endogenous production of NO2-cLA protects against AAA through PRDM16 in VSMC. This work will define PRDM16 as a novel therapeutic target for AAA and establish the basis to develop a feasible new oral therapeutic approach..